The function of a cytokine called GIF or MIF has been unclear for a long time. However, recent studies have demonstrated that a posttranslational modification of this cytokine at C60 is required for the binding to the receptor and for the capability to inhibit B cell Ig switch, BCR-mediated antigen uptake, and IL-4 secretion from CD4 cells. GIF-/- mice displayed enhanced antibody responses to a T-dependent antigen regardless of Ig isotype but normal responses to a T-independent antigen. CD4 cells from GIF-/- mice differentiated toward a Th2 phenotype as compared with wild type cells. GIF receptor was undetectable in resting mouse T and B cells, but after in vitro stimulation the receptor was induced on these cells. GIF receptor appeared to be a 50-52 kDa cell surface protein. To determine whether the biological effects of GIF is mediated through the interaction of GIF and its receptor, anti-receptor mAb will be generated and the cDNA encoding the receptor will be cloned. To define the target cells for this cytokine, the expression of the receptor will be delineated using cells and mRNA samples from various hematopoietic and nonhematopoietic tissues. To clarify the role of GIF in regulating B cell activation in T-B collaboration, HEL-specific B cells from MD4 BCR Tg mice and Ova-specific CD4 cells from DO11.10 TCR Tg mice, either on GIF+/+ or -/- background, will be stimulated in vitro with HEL-Ova conjugate. The secretion of GIF, the induction of its receptor, and the events associated with B cell activation will be analyzed in the course of the cognate T-B interaction. The effects of GIF on BCR-dependent antigen uptake, trafficking, and processing will be analyzed. To determine the role of GIF on cytokine production and Th differentiation of CD4 cells, the expression of GIF receptor and the secretion of GIF upon T cell activation will be analyzed. The source of GIF that regulates Th differentiation will be determined by adoptive transfer experiments using CD4 cells from GIF+/+ and -/- DO11.10 TCR Tg mice and bone marrow chimera constructions. The mechanism by which GIF inhibits Th2 differentiation and/or induces Th1 differentiation will be analyzed with regard to Stat phosphorylation and transcription factors. The role of GIF in regulating Th2-type inflammation will be evaluated in the mouse model of antigen-induced bronchial asthma. These experiments will establish the role of this cytokine in CD4 T cell-mediated immune responses. [unreadable] [unreadable]